Fig. 296 shows a complete dissection of the adult human viscera and vessels concerned in the formation of the foramen, hardened in situ.
The stomach is removed, dividing of course the coronary artery and vein and the left gastro-epiploic artery. The portal vein, hepatic artery and bile-duct are seen entering and leaving the liver at the transverse fissure. Behind them and to the right the vena cava enters the liver. The hepatic artery distributes its pancreatico-duodenal branches to the duodenum and pancreas. The left angle of the Spigelian lobe and the fissure for the ductus venosus appear to the left of the portal vein and hepatic artery. The right angle of the Spigelian lobe and its continuation into the right lobe by means of the caudate lobe is hidden by the structures occupying the transverse fissure. We would enter the beginning of the foramen of Winslow by passing between the vena cava behind, the structures in the transverse fissure (portal vein, hepatic artery and duct) in front, caudate lobe of liver above and duodenum below, the latter in the undisturbed condition of the parts adherent to the right kidney. Continuing to the left the finger would pass between aorta behind, cœliac axis and hepatic artery below and in front, and liver above. These structures bound the permanent and primary narrow channel of communication between the retrogastric or lesser peritoneal space and the general peritoneal cavity, which exists even if a free duodenum and mesoduodenum allow us to lift the intestine away from vena cava and right kidney.
The main facts pertaining to the structure of the lesser peritoneal sac and its connection with the greater peritoneal cavity by means of the foramen of Winslow may be summed up as follows:
Fig. 299.—Schematic sagittal section of abdomen to illustrate the intestinal branches of the abdominal aorta. The gastric and hepatic arteries are shown for the sake of convenience as arising together from the cœliac axis (B), hence the left and right gastro-pancreatic folds carrying these vessels appear fused at their beginning, separating the hepatic recess of the lesser peritoneal sac (A) from the cavity of the omental bursa (C).
The mesogastrium as a whole, expanding originally in the sagittal plane in a fan-shaped manner between the vertebral column and the ventral abdominal wall, from the level of the umbilicus to the septum transversum (diaphragm), divides the cephalic part of the abdominal cavity into a symmetrical right and left half.
[Figs. 172] and [273] represent the membrane as seen in a profile view from the left side. We distinguish the segment dorsad of the stomach as the dorsal mesogastrium, directly continuous with the remaining segments of the common primitive dorsal mesentery, while the portion ventrad of the stomach forms the ventral mesogastrium in which the liver develops. The segment of the ventral mesogastrium between liver and stomach becomes the lesser or gastro-hepatic omentum, while that between liver and ventral abdominal wall forms the falciform or suspensory ligament.
A transection, showing the dorsal and ventral mesogastrium at the level of the fundus of the stomach, is given in Fig. 298. The mesogastria are here seen to be short, while in the schematic [Figs. 291] and [292] the membrane is, for the sake of distinctness, represented as being of considerable extent.
The ventral mesogastrium surrounding the liver and stomach extends caudad to include the first portion of the duodenum. Beyond this point it terminates in a thickened free edge which includes the umbilical vein. This vein extends from the umbilicus to the transverse fissure of the liver (Fig. 297), lying within the umbilical fissure on the caudal surface of the gland.